This invention relates to test systems for electronic devices and, more particularly, to such systems which measure the radio frequency signature of the devices under test and compare this signature to a reference signature to determine the operational status of the device.
Operating unshielded electronic devices, such as integrated circuits, emit an electromagnetic field which may be detected and utilized to determine the operational status of the devices. A radio frequency signature analysis system for determining the functional status of integrated circuit chips has been demonstrated, under laboratory conditions, to be able to detect one faulty circuit device in 8,192. That system utilizes a capacitive pickup probe which is placed by hand on the operating integrated circuit and captures a snapshot of the radio frequency field emitted by the integrated circuit during a defined interval. This field signal is digitized, and processed utilizing a Walsh-Hadamard transform and stored as an N-dimensional vector (N=1024 in the laboratory system) signature representative of the composite radiated field from the individual operating device. Signatures from suspect integrated circuits can be compared with those of known good integrated circuits to identify improperly operating devices. Such a test system is disclosed in U.S. Pat. No. 4,488,301, issued Dec. 11, 1984, which is hereby incorporated by reference.
The present laboratory version of the test system described in U.S. Pat. No. 4,488,301 uses a hand-held capacitive probe to detect the radio frequency field emitted by an operating integrated circuit. The use of such a probe causes repeatability problems resulting from slight variations in the position of the conductive pickup plate in the probe. Although a holding fixture which precisely positions the pickup probe can result in improved repeatability, such a fixture is only practical for shops, depots, or automated inspection and test stations.
It is therefore desirable to provide such a test system with a signature signal pickup means which provides improved reliability and can be used in a wider range of test environments.